import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'RefreshDemo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: '测试滑动刷新下拉'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter++;
    });
  }

  ScrollPhysics scrollPhysics = BouncingScrollPhysics();
  double top = 0;

  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
        appBar: AppBar(
          // Here we take the value from the MyHomePage object that was created by
          // the App.build method, and use it to set our appbar title.
          title: Text(widget.title),
        ),
        body: NotificationListener(
            onNotification: (notificaton) {
              if (notificaton is ScrollStartNotification) {
                print('开始滚动');
              } else if (notificaton is ScrollUpdateNotification) {
                print('update:${notificaton.metrics.pixels}');
                print(
                    'update - maxScrollExtent:${notificaton.metrics.maxScrollExtent}');
                print(
                    'update - minScrollExtent:${notificaton.metrics.minScrollExtent}');
                if (notificaton.metrics.pixels < 0) {
                  setState(() {
                    top = -notificaton.metrics.pixels;
                  });
                }
                //print('update:${notificaton.metrics.pixels}');
              } else if (notificaton is OverscrollNotification) {
                print('overscroll:${notificaton.metrics.pixels}');
              } else if (notificaton is ScrollEndNotification) {
                print('滚动结束');
                setState(() {
                  top = 0;
                });
              } else if (notificaton is ScrollNotification) {
                print(notificaton.metrics.pixels);
              }

              return true;
            },
            child: ScrollConfiguration(
              behavior: MyBehavior(false, false, Colors.red),
              child: Stack(children: [
                Positioned(
                  top: 0,
                  left: 0,
                  right: 0,
                  child: Container(
                    color: Colors.red,
                    height: top,
                    child: Text('刷新有惊喜'),
                  ),
                ),
                CustomScrollView(
                  physics: scrollPhysics,
                  slivers: <Widget>[
                    SliverList(
                      delegate: SliverChildBuilderDelegate((context, index) {
                        return Container(
                          child: Text('$index'),
                        );
                      }, childCount: 100),
                    )
                  ],
                ),
                
              ]),
            )));
  }
}

class MyBehavior extends ScrollBehavior {
  final bool isShowLeadingGlow;
  final bool isShowTrailingGlow;
  final Color _kDefaultGlowColor;

  MyBehavior(
      this.isShowLeadingGlow, this.isShowTrailingGlow, this._kDefaultGlowColor);

  @override
  Widget buildViewportChrome(
      BuildContext context, Widget child, AxisDirection axisDirection) {
    //如果头部或底部有一个 不需要 显示光晕时 返回GlowingOverscrollIndicator
    if (!isShowLeadingGlow || !isShowTrailingGlow) {
      return new GlowingOverscrollIndicator(
        showLeading: isShowLeadingGlow,
        showTrailing: isShowTrailingGlow,
        child: child,
        axisDirection: axisDirection,
        color: _kDefaultGlowColor,
      );
    } else {
      //都需要光晕时  返回系统默认
      return super.buildViewportChrome(context, child, axisDirection);
    }
  }
}
